A number of beneficial-effects have been detected for CLA. Thus, the administration of conjugated linoleic acid decreases the body fat in humans and animals and improves the feed utilization in animals (WO 94/16690, WO 96/06605, WO 97/46230, WO 97/46118). By administering conjugated linoleic acid, for example, allergies (WO 97/32008), diabetes (WO 99/29317) or cancer (Banni, Carcinogenesis, Vol. 20, 1999: 1019-1024, Thompson, Cancer, Res., Vol. 57, 1997: 5067-5072) may also be beneficially affected. Polyunsaturated fatty acids are also added to infant food to “increase the nutritional value” and as essential building blocks which ensure growth and brain development.
Since CLA only occurs naturally in significant quantities in ruminants and their products, such as milk, cheese, etc., there is a great need for alternatives to CLA originating from these animal sources, in order to ensure balanced and healthy nutrition, in particular if the supply with animal fats is reduced, inadequate or if synthetic preparation is too expensive. Commercially, CLAs are currently principally marketed as free fatty acid. Free fatty acids such as CLA, however, generally do not occur naturally as free fatty acids, but are esterified to form biologically active triglycerides. In addition free fatty acids frequently possess disadvantageous sensory properties. For incorporation into foods, for example, triglycerides are also preferred to free fatty acids for technological reasons.
The processes described in the prior art generally consist of two or three process steps in which free fatty acids or their alkyl esters are first prepared and isomerized in order then to transesterify these with glycerol or glycerides under enzymatic or chemical catalysis to form triglycerides.
In the conventional preparation method for free CLA acids, unconjugated linoleic-acid-containing oils (for example sunflower seed oil, soybean oil or safflower oil) are isomerized, for example, with NaOH or KOH in ethylene glycol at 180° C. (Ip C. et al., Cancer Res. 51 (1991) 6118-6124). This process requires superstoichiometric amounts of alkali (based on fatty acids present in the oil) and produces substantial amounts of unwanted CLA isomers (in particular 8t, 10c- and 11c, 13t-CLA). 
EP-839897 describes a process in which, for the isomerization, linoleic acid-containing oils are reacted with KOH in propylene glycol at 150° C. Free CLA acids are obtained which contain only relatively small amounts of unwanted isomers. This process requires superstoichiometric amounts of KOH and corresponding amounts of mineral acids.
In one process, linoleic acid alkyl esters-are isomerized with catalytic amounts (0.3 to 1%) of potassium alkoxide, with CLA alkyl esters being obtained (DE-1156788 and DE-1156789).
To prepare triglycerides, in EP-0779033, linoleic acid is isomerized at 180° C. with NaOH in ethylene glycol to form free CLA and the free CLA is transesterified with palm oil triglycerides using immobilized Mucor miehei lipase. The triglyceride obtained as product contains approximately 8% of each of the two wanted CLA isomers (9c, 11t- and 10t, 12c-) in esterified form.
In some non-enzymatic processes, the esterification of glycerol and the transesterification of natural fats and oils with free CLA acids is carried out with the addition of known esterification catalysts at high temperatures (from 180 to 240° C.) (Mikusch; Farben, Lacke, Anstrichstoffe 4 (1950) 149-159; DE-19718245). The resultant CLA-containing triglycerides, owing to the temperature stress necessary in the process, have a high content of isomers which are unwanted for nutritional uses (in particular 8t,10c- and 11c,13t-CLA fatty acid radicals).
WO 01/18161 describes a solvent-free synthetic process for preparing CLA. The preparation of CLA from oil by alkali isomerization is also described there.
The individual CLA isomers can also be transesterified with the palm oil triglycerides after enrichment of the isomers. In this manner a CLA content of 30% in the triglyceride can be achieved. (McNeill, J. Am. Oil Chem. Soc. 76 (1999) 1265). The transesterification of butter fat with free CLA is based on a similar process, inter alia, immobilized Candida antarctica lipase acting as preferred catalyst (Garcia, Biotechnol. Tech. 12 (1999) 369-373; Garcia, J Dairy Sci 2000, 83:371-377; Garcia, Biotechnology Letters (1998) 20:393-395). In a similar manner, corn oil was also modified using chemically synthesized CLAs using lipase catalysis (Martinez, Food Biotechnology 1999, 13:183-193).
Processes described in the prior art which start from CLAs in the form of free fatty acids for preparing the triglycerides thus, using stoichiometric amounts of bases, release the fatty acids from oils containing non-conjugated polyunsaturated fatty acids and simultaneously carry out the conjugation. In the second process step, conjugated polyunsaturated fatty acids are reacted with glycerol or glycerides to form glycerides containing conjugated, polyunsaturated fatty acids.
Furthermore, in the prior art, in the preparation of glycerides containing conjugated, polyunsaturated fatty acids from glycerides or glycerol by reaction with alkyl esters of conjugated polyunsaturated fatty acids, the alkyl esters of conjugated, polyunsaturated fatty acids are obtained by transesterifying non-conjugated, polyunsaturated fatty acid-containing oils using catalytic amounts of alkali metal bases and superstoichiometric amounts of alcohols to give the alkyl esters of polyunsaturated fatty acids and these are then converted into the alkyl esters of conjugated fatty acids in a second process step using catalytic amounts of alkaline earth metal bases.
The processes described in the prior art thus have the disadvantage that two to three process steps are required, which is an economic disadvantage, to prepare glycerides containing conjugated, polyunsaturated fatty acids.